Methods and Apparatus for Secure and Adaptive Delivery of Multimedia Content

ABSTRACT

Techniques for securely and adaptively delivering multimedia content are disclosed in which a set of alternate access units for each time slot is obtained. Then, the encryption stream index of each access unit from the set of alternate access units of the previous time slot are obtained. An encryption stream index is then assigned to each access unit in the set of alternate access units in the current time slot, such that the encryption index increases over time. Thus, the invention overcomes the problem of encrypting a multimedia stream that may have multiple access units for each time slot by selecting the encryption index for each access unit such that the encryption index increases, regardless of which access unit the delivery system (e.g., server) selects for transmission.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.11/781,699, filed on Jul. 23, 2007, which is a continuation of U.S.application Ser. No. 10/410,455, filed on Apr. 9, 2003, the disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to data delivery techniques and, moreparticularly, to techniques for delivering multimedia content in asecure and adaptive manner.

BACKGROUND OF THE INVENTION

Secure delivery of multimedia content, e.g., audio and video, over anetwork, such as an IP (Internet Protocol) network, has become animportant goal for all involved with such content, e.g., contentauthors, content providers, and content receivers (e.g., clients).Existing approaches attempt to achieve secure delivery of multimediacontent in a number of ways. Some examples are described below.

In an approach referred to as download-based security, encrypted contentis downloaded to a client device in its entirety. In an alternativeapproach referred to as transmission-based security, content isencrypted at the time of transmission. Encrypting the content directlybefore transmission and decrypting directly upon receipt allows thecontent to be streamed, i.e., the client device can process portions ofthe content and is not required to receive the content in its entiretybefore playback.

In another approach referred to as end-to-end security, meta-informationrequired to effectively stream content is extracted before encryption.In this approach, the content creator, or publisher, can encrypt thecontent before transmission to delivery systems. The content remains inthis encrypted form until it reaches the client. The client retrievesrights information and decryption keys from a rights management system.Thus, while the content is not adaptable, the delivery system can streamthe content to the client and end-to-end security can be maintained.

SUMMARY OF THE INVENTION

The present invention provides techniques for securely and adaptivelydelivering multimedia content in a manner which overcomes deficienciesassociated with existing approaches.

In one illustrative aspect of the invention, techniques for processingcontent for delivery in a secure and adaptive manner may include thefollowing steps/operations. It is assumed that a set of alternate accessunits for each time slot is obtained. An encryption stream index is thenassigned to each access unit in the set of alternate access units in thecurrent time slot, such that an encryption index increases over time.For example, the assigning step may include assigning an encryptionindex to each access unit in the set of alternate access units in thecurrent time slot such that an encryption index increases with respectto each encryption index of each access unit from a set of alternateaccess units for a previous time slot. Thus, the invention overcomes theproblem of encrypting a multimedia stream that may have multiple accessunits for each time slot by selecting the encryption index for eachaccess unit such that the encryption index increases, regardless ofwhich access unit the delivery system (e.g., server) selects fortransmission.

Advantageously, the invention overcomes disadvantages associated withexisting multimedia security approaches. By way of example only, thetechniques of the invention serve to avoid: (i) the consumption ofsignificant storage resources at a client device associated with largeobjects, such as video objects (e.g., one problem known to exist in thedownload-based approach); (ii) intermediate devices, such as proxies anddelivery servers, having access to content in its unencrypted form(e.g., one problem known to exist in the transmission-based approach);and (iii) the inability to adapt content to the characteristics of aclient device, or a connection over which the client connects to adelivery system or server (e.g., one problem known to exist in theend-to-end security approach).

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an environment in whichtechniques of the present invention may be implemented;

FIG. 2 is a block diagram illustrating a data processing systemaccording to an embodiment of the present invention;

FIG. 3 is a flow diagram illustrating an overview of an encryption indexassignment methodology according to the present invention;

FIG. 4 is a diagram illustrating an index assignment example accordingto a first embodiment of the present invention;

FIG. 5 is a flow diagram illustrating an encryption index assignmentmethodology according to a first embodiment of the present invention;

FIG. 6 is a diagram illustrating an index assignment example accordingto a second embodiment of the present invention;

FIG. 7 is a flow diagram illustrating an encryption index assignmentmethodology according to a second embodiment of the present invention;

FIG. 8 is a diagram illustrating an index assignment example accordingto a third embodiment of the present invention;

FIG. 9 is a diagram illustrating another index assignment exampleaccording to a third embodiment of the present invention;

FIG. 10 is a flow diagram illustrating an encryption index assignmentmethodology according to a third embodiment of the present invention;and

FIG. 11 is a block diagram illustrating an exemplary computing systemenvironment for implementing a data processing system according to anembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following description will illustrate the invention using anexemplary multimedia content authoring and delivery environment. Itshould be understood, however, that the invention is not limited to usewith any particular type of content authoring and delivery environment.The invention is instead more generally applicable for use with anycontent authoring and delivery environment in which it is desirable toprovide secure and adaptive delivery of authored content.

Referring initially to FIG. 1, a block diagram illustrates anenvironment in which techniques of the present invention may beimplemented. As shown, environment 100 includes a content creationsystem 110, a content delivery system 120, and client device 130. It isto be understood that one or more of the components shown in FIG. 1 maybe coupled to one or more other components shown in FIG. 1 by a networksuch as an IP network (e.g., Internet). However, it is to be furtherunderstood that the techniques of the invention may be implemented inaccordance with other public networks, private networks, and/or insystems that do not employ a network at all.

Thus, in general, multimedia content is created by authors or publishersin accordance with content creation system 110. The created content isthen sent to content delivery system 120. Content delivery system 120then delivers content to client device 130 upon receipt of a requesttherefrom. It is to be appreciated that, while only one client device isshown, there are typically multiple client devices that receive contentfrom content delivery system 120. Similarly, there may be multipledelivery systems delivering the content, possibly using differentdelivery protocols and mechanisms.

Before explaining illustrative embodiments for implementing principlesof the invention and thus further explaining detailed processesperformed by components shown in FIG. 1, some definitions of terms to beused in accordance with such explanations are provided below.

Access Unit: The smallest chunk or portion of multimedia data that has aunique time. For example, a video picture in a video sequence or anaudio frame in a sound track. An access unit may also be referred to asa description.

RTP: Real Time Protocol. A framing method for transporting multimediadata over IP networks in the form of packets.

RTP packet: A chunk or portion of multimedia data as sent over an IPnetwork, prepended with certain information, such as a time stamp and asequence number.

Encryption key: The secret information that is used to encrypt anddecrypt data. A key is typically several bytes, such as seven bytes forthe Data Encryption Standard (DES) and 16 bytes (or more) for theAdvanced Encryption Standard (AES).

Encryption index: An integer value that can be used to start or restartthe encryption or decryption process in the middle of a stream of data.Having this information with the corresponding encrypted data allows forfeatures such as data loss handling, random access, and joining abroadcast.

Referring now to FIG. 2, a block diagram illustrates a data processingsystem according to an embodiment of the present invention. Morespecifically, FIG. 2 illustrates functional components that may be usedin accordance with a content creation system (e.g., content creationsystem 110 of FIG. 1) and a content delivery system (e.g., contentdelivery system 120 of FIG. 1). As will be explained, data processingsystem 200 of FIG. 2 generates a stream that offers a choice frommultiple access units for a single time slot within which the accessunits are to be encrypted.

As shown, a multimedia stream source 210 offers unencoded access units(e.g., frames) to a multi-encoder platform 220. An example of anunencoded video frame (video access unit) is an image with red, green,and blue pixels. This platform 220 generates multiple encoded accessunits for each offered unencoded access unit and passes off the multipleencoded access units to a stream thinner 230. Encoded (e.g., compressed)access units may, for example, be obtained by applying a standard datacompression technique such as MPEG-1, MPEG-2, or MPEG-4. Given use ofone of the compression techniques, say MPEG-4, alternate or multipleencodings corresponding to an access unit may therefore include: (i) aversion of the video frame or image (access unit) encoded via the MPEG-4technique in accordance with a low bandwidth encoder; (ii) a version ofthe video frame or image (access unit) encoded via the MPEG-4 techniquein accordance with an intermediate bandwidth encoder; and (iii) aversion of the video frame or image (access unit) encoded via the MPEG-4technique in accordance with a high bandwidth encoder. The idea beingthat alternate versions of the access unit are made available so thatthe appropriate access unit can be provided to a client device that bestmatches a parameter or characteristic associated with the client deviceor connection, e.g., the access unit encoded at a low bandwidth isprovided to a client device with limited bandwidth capability, theaccess unit encoded at an intermediate bandwidth is provided to a clientdevice with intermediate limited bandwidth capability, and so on. Thelevel of bandwidth (e.g., low, intermediate, high) is relative to themultimedia application and client devices receiving the multimedia. Itis to be understood that the above example of a form of multipleencodings is only one example of a form of multiple encodings and, thus,the invention is not limited to any particular form.

Stream thinner 230 can remove certain access units for each time slotbased upon some criterion. One example of stream thinning or access unitremoval is the case where a time slot contains several access units thatare very similar in properties such as size. In that case, those similaraccess units could all be represented by a single selection from thosesimilar access units. So, an access unit can be discarded from onestream for a certain time slot, and an access unit from another streamin the same time slot is used instead. The thinned access unit streamsare input into encryptor 240, where they are encrypted. The output ofencryptor 240 is finally sent to an output device 250, such as a networkprotocol formatter or a file writer.

In terms of FIG. 1, it is to be appreciated that the multi-encoderplatform 220, the stream thinner 230, and the encryptor 240 may beimplemented as part of content creation system 110, while the networkprotocol formatter 250 may be implemented as part of content deliverysystem 120. However, the functional components may be implemented inaccordance with other arrangements.

The multi-encoder platform and stream thinner operations may beperformed via a number of known multiple encoding generation and streamthinning techniques. By way of one example only, techniques described inJ. G. Apostolopoulos et al., “Unbalanced Multiple Description VideoCommunication Using Path Diversity,” IEEE International Conference onImage Processing (ICIP), Thessaloniki, Greece, October 2001, thedisclosure of which is incorporated by reference herein, may be employedto generate multiple encodings of the multimedia content. An example ofa stream thinning technique that may be employed is described in Z. L.Zhang et al., “Efficient Selective Frame Discard Algorithms for StoredVideo Delivery Across Resource Constrained Networks,” Proceedings ofIEEE INFOCOM Conference, vol. 2, pp. 472-479, 1999, the disclosure ofwhich is incorporated by reference herein.

In a preferred embodiment, techniques described in U.S. patentapplication Ser. No. 10/406,715 (entitled “Multiple Description Hintingand Switching for Adaptive Media Services”), filed Apr. 8, 2003 andcommonly assigned, and in U.S. patent application Ser. No. 10/409,303(entitled “System and Method for Resource-Efficient Live Media Streamingto Heterogeneous Clients”), filed Apr. 3, 2003 and commonly assigned,the disclosures of which are incorporated by reference herein, may beemployed for the multiple encoding generation and stream thinningoperations.

More specifically, in the above-referenced patent applications (namely,10/409,303 and 10/406,715), techniques which allow adaptation, withoutrequiring access to unencrypted content, are provided. The techniquesenable adaptation by creating multiple encodings (also referred to asdescriptions) of portions (access units) of the content, and packagingthese descriptions with meta-data that enables adaptation at thedelivery server. Adaptation occurs at the delivery server by selectingand transmitting the encoding which best meets the connection bandwidthand packet loss conditions, as well as the client devicecharacteristics.

In general, the techniques of the above-referenced patent applicationsmay be implemented in the multi-encoder platform 220 and stream thinner230 as follows. A live media source feeds a multi-encoder station, whichoutputs several descriptions or bitstreams of the source signal. Thesebitstreams have different characteristics in terms of bit-rate orstructure (e.g., encoding modes), in order to cover the requirements ofthe different clients. The bitstreams are basically a series ofcompressed data units (e.g., video frames). The different encodingparameters generate several compressed descriptions of the original dataunits. In general, the clients receive one description for each dataunit, but these descriptions can come from different compressedbitstreams. The number of descriptions can also vary depending on thetransmission conditions, and data units can even be skipped if theavailable bandwidth becomes too small. The encoded bitstreams are sentto a stream thinner, which dynamically decides which descriptions willbe sent over the network to the clients. The stream thinner can decideto send all the bitstreams, one complete bitstream and parts of theothers, or any combination it will determine as being appropriate tooptimally serve all the receivers. The stream thinner implements apruning algorithm based on the media content, and on the feedback (e.g.,Real Time Control Protocol or RTCP) it receives from the network aboutthe actual infrastructure configuration and client capabilities.Basically, if descriptions from different streams are similar enough,one or more of them will be discarded without penalizing the quality ofservice perceived by the receivers.

While preferred and other illustrative embodiments are described above,it is to be understood that the invention is not limited to anyparticular multiple encoding generation and/or stream thinningtechniques.

In the following description of illustrative embodiments, a multimediastreaming network that may exhibit data loss is preferably assumed. Anexample of such a network protocol is RTP over User Datagram Protocol(UDP), where data packets may be dropped enroute from server to client.

When encrypting multimedia content in such an application environment,it is preferable to use an encryption method that allows decryptionwhich is independent of previously decrypted data. Examples of suchencryption methods include “SEAL” (as described in P. Rogaway et al., “ASoftware-Optimized Encryption Algorithm,” Journal of Cryptology, vol.11, no. 4, pp. 273-287, 1998, the disclosure of which is incorporated byreference) and “Block Cipher in Counter Mode” (as described in B.Schneier, “Applied Cryptography,” John Wiley & Sons, 1996, thedisclosure of which is incorporated by reference). Examples of blockciphers are DES (e.g., as described in the above-referenced B. Schneieret al. text) and AES (e.g., as described in NIST FIPS 197, thedisclosure of which is incorporated by reference herein). Both for“Block Cipher in Counter Mode” and for “SEAL,” the cipher text can bedecrypted at any location in the cipher text stream, given that exactlocation in the stream, i.e., the byte offset or the “encryption index.”Therefore, to be able to handle data loss, the invention preferablyemploys (e.g., in accordance with encryptor block 240) an encryptionmethod such as described above, and makes the encryption index availablefor decryption. This means that for a protocol like RTP over UDP,typically the encryption index is sent with every RTP packet, thusallowing each packet to be independently decrypted.

Note that having an encryption index also enables random access, thusallowing searching of a multimedia presentation file and joining abroadcasted multimedia stream at a point somewhere other than at thebeginning of the stream, e.g., midstream.

Combining access unit interchangeability (i.e., selection of an encodingof an access unit from among multiple encodings of the access unit) andend-to-end security imposes some constraints on how the encryption indexis chosen. As a cryptographic constraint, one should adhere to the ruleof not using the same index twice for the same encryption key. Violatingthis rule introduces a cryptographic weakness that will make the systeminsecure. That constraint can be overcome by encrypting alternate accessunits (descriptions) with different keys. However, it should be takeninto account that one may not want to transmit a complete index (e.g.,132 bits) by relying on an index that always increases only minimallyfrom packet to packet. Sending a complete index would increase theoverhead from a mere 16-24 bits to 132 bits, which can be deemedunacceptable, especially if packets are small.

Therefore, in accordance with the present invention, the problem ofencrypting a multimedia stream that may have multiple access units foreach time slot is overcome by selecting the encryption index for eachaccess unit such that the encryption index always increases, regardlessof which access unit the delivery system (e.g., server) selects fortransmission. It is to be appreciated that such selection or assignmentof encryption indexes may be performed in encryptor 240 of FIG. 2.

Accordingly, in general, a methodology of delivering content in a secureand adaptive manner may include using a set of alternate access units(e.g., multiple encodings of an access unit) for each time slot. Then,the encryption stream index of each access unit from the set ofalternate access units of the previous time slot are obtained (e.g.,retrieved from storage). An encryption stream index is then assigned toeach access unit in the set of alternate access units in the currenttime slot, such that the encryption index increases over time, e.g., ascompared to indexes assigned to access units of the previous time slot.

The following description will provide explanation of an overview of anencryption index assignment methodology of the present invention whichmay accomplish the above solution, followed by explanation ofembodiments for use in three different cases (i.e., method 1, method 2,and method 3). As will be seen, each case may assign the encryptionindex to each access unit in each time slot differently.

Referring now to FIG. 3, a flow diagram illustrates an overview of anencryption index assignment methodology according to the presentinvention. It is to be understood that the methodology in FIG. 3 depictsan overview of how encryption index assignment methodologies (i.e.,method 1, method 2, and method 3) associated with each case may beinitiated.

The following notation shall be used to describe encryption indexassignment operations. At any given time slot i, a set of streams isdefined as having N(i) access units, the encryption indexes of theseN(i) access units are C(1,i) through C(N(i),i) and the correspondingsizes of the access units are L(i) through L(N(i),i). M refers to arunning intermediate encryption index.

As shown in methodology 300 of FIG. 3, the process begins at block 302.In step 304, i and M are initialized to one and zero, respectively. Instep 306, the process determines whether there are more time slots to beconsidered. Assuming there are, the process retrieves the N(i) accessunits for time slot i. Step 310 determines whether there are multiplekeys for the time slot. If no, then indexes are assigned in step 312 inaccordance with method 2 (as will be explained below in the context ofFIG. 7). If there are multiple keys for the time slot, step 314determines whether one stream may not have gaps (as will be definedbelow). If yes, then indexes are assigned in step 316 in accordance withmethod 3 (as will be explained below in the context of FIG. 10). If astream may have gaps (i.e., step 314 yields a “no” response), thenindexes are assigned in step 318 in accordance with method 1 (as will beexplained below in the context of FIG. 5). Then, in step 320, the timeslot variable is incremented by one and if there are more time slots toconsider (step 306), the process repeats. If there are no more timeslots to consider, then the process ends at block 322. Thus, it is to beappreciated that methods 1, 2 and 3 ensure that the indexes of thecurrent time slot increase as compared with those of the previous timeslot.

Method 1: Each Stream has a Different Key

In the most common situation, a different key is used for each alternateaccess unit (or description) for any given time slot. If each accessunit is represented as a horizontal bar with a size proportional to thelength of that access unit, the solution can be depicted as shown inFIG. 4.

More specifically, FIG. 4 is a diagram illustrating an index assignmentexample according to method 1 (step 318 of FIG. 3). As shown, in thefirst time slot (i), there are three access units, the longest one beingthe first access unit. In the second time slot (i+1), there are twoaccess units, the longest one being the second access unit. In the thirdtime slot (i+2), there are 3 access units, the longest one being thethird. Finally, in the fourth time slot (i+3), there are two accessunits, the longest one being the first access unit. In FIG. 4, since thehorizontal axis represents the running intermediate encryption index M,the encryption index can be seen increasing in value from left to right,according to the accumulative values of the access unit sizes from onetime slot to the next. Such index assignment may be accomplished inaccordance with the process depicted in FIG. 5.

Referring now to FIG. 5, a flow diagram illustrates an encryption indexassignment methodology according to method 1. The methodology 500 beginsat block 502. It is to be appreciated that steps 504, 506, 508, 514 and516 are respectively identical to steps 304, 306, 308, 320 and 322 ofFIG. 3, and therefore their explanation will not be repeated.

Thus, in accordance with steps 510 and 512, the process takes theencryption stream index of each access unit from the set of alternateaccess units of the previous time slot and adds the corresponding accessunit lengths to the indexes from the previous time slot (i.e., calculateM=M+max {L_(i)(n)}, n=1, . . . , N_(i)). Then, the encryption streamindex of each access unit in the current time slot is set equal to orlarger than the maximum of the computed sums.

So, if the indexes of the access units for the first time slot i=1 are:

C(1,1)=. . . =C(N(1),1)=0,

the process may calculate the indexes at time slot (i+1) to be all thesame and equal to:

C(1,i+1)=. . . =C(N(i+1)=max_(n=1, . . . , N(i))) {C(n,i)+L(n,i)}

It should be noted here that in this exemplary equation the encryptionindex is assigned as equal to the maximum, but in general an encryptionindex that is equal to or larger than this value is a valid value. Thatis, while the example selects an index value equal to the maximum, anyincrement larger than that value may be employed.

Method 2: Each Stream Uses the Same Key

In case a very simple key management system is used that allows only asingle key per stream, then all alternate streams must use the same key.In that situation, the same index should not be used more than once and,thus, the index is incremented from one access unit to another asdepicted in FIG. 6.

So the indexes of time slot (i+1) can be calculated as:

C(1,i+1)=C(N(i),i)+L(N(i),i)

C(2,i+1)=C(1,i+1)+L(1,i+1)

. . .

C(N(i+1),i+1)=C(N(i+1)−1,i+1)+L(N(i+1)−1,i+1)

The index of the first access unit for the first time slot i=1 is:

C(1,1)=0

A flow diagram of this process is shown in FIG. 7. More specifically,FIG. 7 is a flow diagram illustrating an encryption index assignmentmethodology according to a second embodiment of the present invention(e.g., method 2 as referred to in step 312 of FIG. 3). The methodology700 begins at block 702. Again, it is to be appreciated that steps 704,706, 708, 720 and 722 are respectively identical to steps 304, 306, 308,320 and 322 of FIG. 3, and therefore their explanation will not berepeated.

Thus, in accordance with steps 710 through 718, the process sets theencryption stream index of the first access unit in the set of alternateaccess units with the earliest time slot to an initial value. This isshown in step 714, where the first access unit (n=1, where n refers to avariable representing the number of the access unit in the subject setwhich is set to one in step 710) for the first time slot (i=1) isassigned the initial value for M, which was set in step 704 to the valueof M=0. Then, in step 716, the last computed encryption stream index isobtained and the access unit length corresponding to the access unitthat the encryption stream index was computed for is added to the lastcomputed encryption stream index. Then, the encryption stream index ofthe next access unit is set equal to or larger than the computed sumvalue. It is to be understood that the next access unit (n=n+1, asincremented in step 718) is defined as the next access unit in the samealternate set or, if all encryption stream indexes in that the same sethave been calculated, as tested for in step 712, the next access unit isthe first access unit of the set of alternate access units of the nexttime slot.

Again, it should be noted here that in this exemplary equation theencryption index is assigned as equal to the maximum, but in general anencryption index that is equal to or larger than this value is a validvalue. That is, while the example selects an index value equal to themaximum, any increment larger than that value may be employed.

Method 3: One Stream may not have Index Gaps

There are certain situations where a multimedia stream isself-contained, is delivered in a loss free environment (e.g.,downloaded), and played back as is. An example of such a case is an MP3audio file. When such a stream is encrypted with an indexed streamcipher and the index is used without gaps, i.e., the index of an accessunit is exactly equal to the index plus the length of the previous one,the stream can be decrypted and played back by simply knowing the keyand the index for the first byte (access unit) of the stream. Sincethere are no losses, it is not necessary to insert the index as is donein RTP over UDP. In that case, one alternate access unit from the set ofchoices is always part of that self-contained multimedia stream, e.g.,MP3.

The situation is illustrated in FIG. 8. That is, FIG. 8 depicts an indexassignment example for when one stream must have continuous indexeswithout gaps. In this example, the first access unit is assumed to bepart of this “main” stream, i.e., the desired stream without any gaps inthe encryption index, denoted as 802 in FIG. 8.

It can be seen that a special case exists when an alternate access unitthat is not part of the “main” stream is larger than the correspondingmain stream access unit. In that case, the key that was used for the“too-long” access unit is not used. The encryption indexes arecalculated here in the same manner as in the case where there is noconstraint to a stream without gaps. If the other alternate access unitsare considered part of a media stream, this solution can thus be viewedas a key change.

In the case where a key change is not desirable or not possible, forexample, when the alternate access units are generated as part ofalternate streams, each access unit uses exactly a single key. In thatcase, the server may not always have total freedom in selecting accessunits (or streams in this case). An example of this is shown in FIG. 9.That is, FIG. 9 depicts an index assignment example for when one streammust have continuous indexes without gaps and no key change is allowed.

In this example, if the server sent the “problem” access unit for timeslot (i+1), denoted as 902 in FIG. 9, then from time slot (i+2), it isnot allowed to select the access unit from the “main” stream with thecontinuous indexes, denoted as 904 in FIG. 9. Note that in the exampleof FIG. 6, it is possible to choose an index of the third stream, suchthat it is possible to select that access unit after the “problem”access unit is selected.

A flow diagram of this process is shown in FIG. 10. More specifically,FIG. 10 is a flow diagram illustrating an encryption index assignmentmethodology according to a third embodiment of the present invention(e.g., method 3 as referred to in step 316 of FIG. 3). The methodology1000 begins at block 1002. Again, it is to be appreciated that steps1004, 1006, 1008, 1026 and 1028 are respectively identical to steps 304,306, 308, 320 and 322 of FIG. 3, and therefore their explanation willnot be repeated.

Thus, in accordance with steps 1010 through 1024, the process sets theencryption stream index of the access unit of the special stream fortime slot i equal to the value M in step 1010. The value M wasinitialized to the zero in step 1004. The special stream is defined asthat stream that is selected to not have encryption index gaps and willbe assigned the stream index n=1 in the example of FIG. 10. Then, instep 1016, the process tests if an extra key may be used, and if so, theencryption stream index of the other access units in the same time slotare set equal to or greater than the encryption stream index of theaccess unit of the special stream, as shown in step 1022. If no extrakey may be used, in step 1018, the encryption index of the access unit nin slot i is set to the maximum of the encryption index M of the specialstream (which has index n=1) and the sum of the previous access unitencryption index and the corresponding size. Steps 1014 and 1020 havethe same function as steps 712 and 718 of FIG. 7. Note that n is set totwo (n=2) in step 1012 because n=1 was calculated in step 1010 as themain stream.

Again, it should be noted here that in this exemplary equation theencryption index is assigned as equal to the maximum, but in general anencryption index that is equal to or larger than this value is a validvalue. That is, while the example selects an index value equal to themaximum, any increment larger than that value may be employed.

Referring now to FIG. 11, a block diagram illustrates an exemplarycomputing system environment for implementing systems and correspondingmethodologies of the invention, e.g., as described above in the contextof FIGS. 1-10. For example, it is to be understood that the computingsystem shown in FIG. 11 may represent a computing system used toimplement a content creation system and/or a content deliverysystem/server as shown in FIG. 1 (as well as components thereof shown inFIG. 2). The computing system in FIG. 11 may also represent a computingsystem used to implement a client device as shown in FIG. 1. One or moreof such computing systems may communicate over a distributed network.The network may be any suitable network across which the computersystems can communicate, e.g., the Internet or Word Wide Web, local areanetwork, etc. However, the invention is not limited to any particulartype of network. In fact, it is to be understood that the computersystems may be directly linked without a network.

As shown, the computing system 1100 comprises a processor 1102, memory1104 and I/O devices 1106, all coupled via a computer bus 1108. Itshould be understood that the term “processor” as used herein isintended to include one or more processing devices, including a centralprocessing unit (CPU) or other processing circuitry, e.g., digitalsignal processor, application-specific integrated circuit, etc. Also,the term “memory” as used herein is intended to include memoryassociated with a processor or CPU, such as RAM, ROM, a fixed,persistent memory device (e.g., hard drive), or a removable, persistentmemory device (e.g., diskette or CDROM). In addition, the term “I/Odevices” as used herein is intended to include one or more input devices(e.g., keyboard, mouse) for inputting data to the processing unit, aswell as one or more output devices (e.g., CRT display) for providingresults associated with the processing unit.

It is also to be understood that the computing system illustrated inFIG. 11 may be implemented in the form of a variety of computerarchitectures depending on the functions performed thereby, e.g., aserver, a personal computer, a microcomputer, a minicomputer, a personaldigital assistant, a cellular phone, etc. However, the invention is notlimited to any particular computer architecture.

Accordingly, software instructions or code for performing themethodologies of the invention, as described herein, may be stored inone or more of the associated memory devices, e.g., ROM, fixed orremovable memory, and, when ready to be utilized, loaded into RAM andexecuted by the CPU.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may bemade by one skilled in the art without departing from the scope orspirit of the invention.

1. A method of processing content for delivery in an information system,wherein the content is representable as access units, the methodcomprising the steps of: obtaining a set of alternate versions of anaccess unit for a current time slot associated with the content; andassigning, by a processor of the information system, an encryption indexto each access unit in the set of alternate versions of the access unitin the current time slot such that an encryption index increases overtime.
 2. The method of claim 1, wherein the assigning step furthercomprises assigning an encryption index to each access unit in the setof alternate versions of the access unit in the current time slot suchthat an encryption index increases with respect to each encryption indexof each access unit from a set of alternate versions of an access unitfor a previous time slot.
 3. The method of claim 1, wherein eachalternate version of the access unit uses a different encryption key. 4.The method of claim 1, wherein each alternate version of the access unituses the same encryption key.
 5. The method of claim 4, wherein theassigning step further comprises the steps of: setting the encryptionindex of the first access unit in the set of alternate versions of theaccess unit with the earliest time slot to an initial value; obtainingthe last computed encryption index and computing a sum by adding theaccess unit length corresponding to the access unit for which theencryption index was computed; and setting the encryption index of thenext access unit equal to or larger than the computed sum.
 6. The methodof claim 5, wherein a next access unit is defined as the next accessunit in the same alternate set or, when encryption indexes in the samealternate set have been assigned, the next access unit is the firstaccess unit of the set of alternate versions of the access unit of thenext time slot.
 7. The method of claim 1, wherein the encryption indexof each access unit of a particular stream of access units is equal tothe sum of the encryption index of the previous access unit plus thelength of the previous access unit.
 8. The method of claim 7, whereinthe particular stream of access units comprises a stream of access unitsselected to not have an encryption index gap.
 9. The method of claim 7,wherein the assigning step further comprises the steps of: obtaining theencryption index of the access unit of the particular stream for a giventime slot; and setting the encryption index of the other access units inthe same time slot equal to or greater than the encryption index of theaccess unit of the particular stream.
 10. The method of claim 1, whereinthe content is multimedia content.
 11. The method of claim 1, whereinthe obtaining and assigning steps are performed in accordance with acontent creation system.
 12. The method of claim 11, wherein accessunits and encryption indexes are provided to at least one deliveryserver for subsequent delivery to at least one client device. 13.Apparatus for processing content for delivery in an information system,wherein the content is representable as access units, the apparatuscomprising: a memory; and at least one processor coupled to the memoryand operative to: (i) obtain a set of alternate versions of an accessunit for a current time slot associated with the content; and (ii)assign an encryption index to each access unit in the set of alternateversions of the access unit in the current time slot such that anencryption index increases over time.
 14. The apparatus of claim 13,wherein the assigning operation further comprises assigning anencryption index to each access unit in the set of alternate versions ofthe access unit in the current time slot such that an encryption indexincreases with respect to each encryption index of each access unit froma set of alternate versions of an access unit for a previous time slot.15. The apparatus of claim 13, wherein each alternate access unit uses adifferent encryption key.
 16. The apparatus of claim 13, wherein eachalternate version of the access unit uses the same encryption key. 17.The apparatus of claim 16, wherein the assigning operation furthercomprises: setting the encryption index of the first access unit in theset of alternate versions of the access unit with the earliest time slotto an initial value; obtaining the last computed encryption index andcomputing a sum by adding the access unit length corresponding to theaccess unit for which the encryption index was computed; and setting theencryption index of the next access unit equal to or larger than thecomputed sum.
 18. The apparatus of claim 17, wherein a next access unitis defined as the next access unit in the same alternate set or, whenencryption indexes in the same alternate set have been assigned, thenext access unit is the first access unit of the set of alternateversions of the access unit of the next time slot.
 19. The apparatus ofclaim 13, wherein the encryption index of each access unit of aparticular stream of access units is equal to the sum of the encryptionindex of the previous access unit plus the length of the previous accessunit.
 20. The apparatus of claim 19, wherein the particular stream ofaccess units comprises a stream of access units selected to not have anencryption index gap.
 21. The apparatus of claim 19, wherein theassigning operation further comprises: obtaining the encryption index ofthe access unit of the particular stream for a given time slot; andsetting the encryption index of the other access units in the same timeslot equal to or greater than the encryption index of the access unit ofthe particular stream.
 22. The apparatus of claim 13, wherein thecontent is multimedia content.
 23. The apparatus of claim 13, whereinthe obtaining and assigning operations are performed in accordance witha content creation system.
 24. The apparatus of claim 23, wherein accessunits and encryption indexes are provided to at least one deliveryserver for subsequent delivery to at least one client device. 25.Apparatus for processing content for delivery in an information system,the apparatus comprising: a content creation system operative to: (i)obtain a set of alternate versions of an access unit for a current timeslot associated with the content; and (ii) assign an encryption index toeach access unit in the set of alternate versions of the access unit inthe current time slot such that an encryption index increases over time.26. An article of manufacture for processing content for delivery in aninformation system, comprising a machine readable medium containing oneor more programs which when executed implement the steps of: obtaining aset of alternate versions of an access unit for a current time slotassociated with the content; and assigning an encryption index to eachaccess unit in the set of alternate versions of the access unit in thecurrent time slot such that an encryption index increases over time.